[sheepdog] [PATCH v2 1/2] sheep, dog: make recycling VID selectable

[Liu Yuan]

On Tue, Mar 17, 2015 at 03:55:56AM +0000, moritakzt at nttdata.co.jp wrote:
> > > > I'm still not sure which code in vdi_lookup() is a problem.  The
> > > > problem happens even when we disable VID garbage collection?
> > >
> > > vdi_lookup() becomes a problem if Hitoshi's patch is enabled after he
> > > fixes a fatal bug of new algorithm.
> 
> I don't think Hitoshi says he will enable the new algorithm by default
> after the fatal bug is fixed.  There is a performance problem as you mentioned,
> and I'm fine with making it disabled by default in future.

Okay, I'm fine with it too. 

> > 
> > I need to add that, old sheep can reuse vid by checking inode's name, so
> > vid recycling is unnecessary. It is proved simple and reliable, at the cost
> > of allow deleted inodes stored on the storage, but the space overhead is
> > too small to notice.
> 
> If you are talking about reverting 21549a1b, it sounds wrong - it's not a
> subtle bug fix but a critical one.
> The old algorithm corrupts inode objects if we don't add --no-share option, no?

It only corrupts data objects I think, but yes, it is problematic.

> Even if you think it's a corner use case, there is no technical way
> to prevent users from doing the operation.

Okay, keep old algorithm as a in-house patch sounds better.

Yuan